Novel waste heat and oil recovery system in the finishing treatment of the textile process for cleaner production with economic improvement

In the textile industry, reactive dyeing requires large volumes of hot water, which increases cost and energy consumption. Although the waste heat of the exhaust gas from the stentering process can be recovered to reduce cost and energy consumption, fiber dust and oil mist inside the exhaust gas cause problems such as fouling and clogged pores. Hence, a novel waste heat and oil recovery system in the finishing treatment of the textile process is proposed for cleaner production with economic improvement. The proposed system comprises the following steps: (a) The exhaust gas is split by the electrostatic precipitator (ESP) at a certain ratio through optimization as its exhaust gas throughput is a key deciding variable for cost and profit. (b) A mathematical model of the overall cost, including profits from oil recovery and energy savings attributed to waste heat recovery, total capital investment, and total product cost attributed to the additional ESP installation, is designed to identify an optimal split ratio. (c) Fiber dust and oil mist are removed from the exhaust gas split at the optimal ratio using the ESP and then recycled as regenerated oil. Waste heat is recovered from the treated gas after the fiber dust and oil mist are recovered as regenerated oil through the heat exchange in the air to water heat exchanger; this recovered heat is supplied to the dyeing process to minimize the energy required for heating the water. (d) Finally, VOCs and the remaining pollutants are removed by activated carbon adsorption from the low-temperature-treated gas after the waste heat is recovered. These processes recover waste heat and oil and achieve process stability and efficiency improvements because of the removal of oil mist, fiber dust, and VOCs. As a result, the overall cost can be reduced by 10.2% based on the recovered waste heat and oil, and the fiber dusts, odor, and VOCs are removed by 95%, 89.86%, and 96.28%, respectively.